Method and device for measuring inner diameter dimension of works

ABSTRACT

A method and a device for measuring the inner diameter dimension of a work capable of easily and accurately measuring the inner diameter dimension of the work with a simple structure; the method, comprising the steps of feeding compressed air to the inner peripheral part of a master with a known inner diameter dimension to detect a back pressure, calculating back pressure characteristics showing a relation between the inner diameter dimension and the back pressure from the measured result, feeding compressed air to the inner peripheral part of the work based to be measured to detect a back pressure, and measuring the inner diameter characteristics, whereby the inner diameter dimension of the work can be measured without rotating the work.

TECHNICAL FIELD

The present invention relates to a method and device for measuring innerdiameter dimension of works. More particularly, it relates to a methodand device for measuring inner diameter dimension of fine cylindricalworks such as ferrules.

BACKGROUND ART

Conventionally, to measure inner diameter dimension of a finecylindrical work such as a ferrule, the operator inserts pin gauges ofpredetermined sizes in an inner periphery of the work. For automaticmeasurement, the work is placed on a V table or the like, the work isrotated with a probe of a contact type displacement gauge kept incontact with its inner periphery, and the inner diameter dimension ofthe work is determined from the amount of displacement of the probe.Alternatively, as disclosed in Japanese Patent Application PublicationNo. 8-29642, Japanese Patent Application Publication No. 10-227619, andJapanese Patent Application Publication No. 6-174433, for example, thework is placed on a V table or the like, images of its end face arepicked up with a CCD camera while it is rotated, and the resulting imagedata is subjected to image processing to determine the inner diameterdimension of the work.

However, the method which uses pin gauges has the drawback of requiringthe operator to expend a great deal of effort measuring each workmanually. Also, it has the drawback of lacking accuracy because ofmanual work. Furthermore, it has the drawback that the pin gages, whichare inserted, get worn as measurements are taken repeatedly, resultingin inaccurate measurements.

On the other hand, the method which uses automatic measurements has thedrawback of taking time for measurements because the work must berotated for each measurement. Also, it has the drawback of needing amechanism for rotating the work, resulting in increased equipment size.Furthermore, it has the drawback that the V table or the like gets worn,resulting in inaccurate measurements because the V table or the like isrotated with a work mounted on it. Besides, it has the drawback that acontact type displacement gauge, which involves inserting the probe inthe inner periphery of the work, cannot measure small-diameter workssuch as ferrules because there are limits to diameters that can bemeasured. On the other hand, the method which uses image processing hasthe drawback of being able to measure only end face diameters.

The present invention has been made in view of the above problems andhas an object to provide an inner diameter measuring method and devicewhich can measure inner diameter dimensions of works easily andaccurately with a simple configuration.

SUMMARY OF THE INVENTION

In order to attain the above object, the present invention is directedto an inner diameter measuring method for measuring inner diameterdimension of cylindrical works, characterized by comprising the stepsof: supplying compressed air to an inner periphery of a cylindricalmaster whose inner diameter dimension is known, detecting its backpressure, and thereby calculating a back pressure characteristic whichrepresents a relationship between the inner diameter dimension and backpressure; and supplying compressed air to the inner periphery of thework to be measured, detecting its back pressure, and thereby measuringthe inner diameter dimension of the work according to the back pressurecharacteristic.

The present invention supplies compressed air to the inner periphery ofa work, detects changes in its back pressure, and thereby measures theinner diameter dimension of the work. The present invention can takemeasurements in a short time because there is no need to rotate thework. Also, it always gives accurate and stable measurements over a longperiod of use because no wear occurs. Also, it can make device compactbecause it does not need a mechanism for rotating the work.

Also, the work may be 0.05 mm to 1 mm in inner diameter.

The present invention is extremely useful in measuring the innerdiameter dimension of fine-diameter works ranging from 0.05 mm to 1 mmin inner diameter because it does not need to insert a probe in theinner,periphery of the work to be measured unlike conventional methods.

Regarding the back pressure characteristic, an optimum value may becalculated by a statistical technique using a plurality of masters whichhave some uncertainties.

Even if masters have uncertainties, the present invention providesaccurate measurements by reducing the effect of uncertainties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an overall configuration of an innerdiameter measuring device according to the present invention;

FIGS. 2( a) and 2(b) are longitudinal sections showing a configurationof a measuring table;

FIG. 3 is a side section showing a configuration of a work;

FIG. 4 is a block diagram showing a configuration of a calibrationmechanism;

FIG. 5 is a longitudinal section of a measuring table equipped with asealing device; and

FIG. 6 is a longitudinal section of a measuring table equipped with anend-face flaw detector.

THE PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

Embodiments of a method and device for measuring inner diameterdimension of works according to the present invention will be describedbelow with reference to the drawings.

FIG. 1 is a schematic view showing an overall configuration of an innerdiameter measuring device according to the present invention. As shownthe drawing, the inner diameter measuring device comprises a measuringunit 10, feeding unit 12, recovery unit 14, master storage unit 16,transport unit 18, and control unit 70 and measures the inner diameterdimension of fine cylindrical works such as ferrules.

The measuring unit 10 measures the inner diameter dimension of the worksW. The measuring unit 10 comprises a plurality of measuring tables 20for holding the works W, and a plurality of air micrometers 22 formeasuring the inner diameter dimensions of the works W held in themeasuring tables 20.

As shown in FIGS. 2( a) and 2(b), the measuring table 20 comprises ameasuring table body 24, pressing ring 26, retaining ring 28, andpressing device (not shown).

The measuring table body 24 is installed vertically and an air supplychannel 30 is formed in the center of it. In the upper surface of themeasuring table body 24 is a circular recess 32, at the center of whichis a work receiving hole 34 with a predetermined depth. The workreceiving hole 34 is provided concentrically with the air supply channel30 and is approximately equal in diameter to the work W measured.

The pressing ring 26 has a work passage hole 36 slightly larger indiameter than the work formed in itself along its axis. The pressingring 26 is fitted in the recess 32 formed in the upper surface of themeasuring table body and is supported in the recess 32 in such a way asto be slidable in the axial direction with the inner surface of therecess 32 serving as a guide surface. On the lower surface of thepressing ring 26 is a pressing surface 38 tapering toward the center andcontacting the retaining ring 28.

The retaining ring 28 is made of an elastic material and contained inthe recess 32 formed in the upper surface of the measuring table body24. It is mounted concentrically with the work receiving hole 34. Whenpressed against the pressing surface 38 of the pressing ring 26, theretaining ring 28 is squeezed, contracting its inner diameter. Undernormal conditions (no-load conditions), the retaining ring 28 has alarger inner diameter than the outside diameter of the work W measured.Thus, the work W is inserted in the retaining ring 28 almost withouttouching the latter.

The pressing device (not shown) comprises, for example, a cylinder andpresses the pressing ring 26 toward the measuring table body 24.

On the measuring table 20 with the above configuration, when the work Wis inserted in the work passage hole 36 of the pressing ring 26, the tipof the work W is inserted in the work receiving hole 34 formed in themeasuring table body 24, as shown in FIG. 2( a). In this sate, when thepressing ring 26 is pressed by the pressing device (not shown) towardthe measuring table body 24 as shown in FIG. 2( b), the retaining ring28 is squeezed against the pressing surface 38 of the pressing ring 26,contracting its inner diameter. Consequently, the outer surface of thework W is clamped by the retaining ring 28, holding the work W to themeasuring table 20. Also, the retaining ring 28 comes into intimatecontact with the outer surface of the work W, providing a seal betweenthe work W and work receiving hole 34.

To dismount the work W, the pressing ring 26 is released. Consequently,the pressing ring 26 returns to its original position by the elasticrestoring force of the retaining ring 28 while the retaining ring itselfrecovers its original diameter by its elastic restoring force. Thisreleases the work W from clamping to make it removable.

The air micrometer 22 comprises an air source 40, regulator 42, A/Econverter 44, and controller 46 as shown in FIG. 1.

The air source 40 supplies compressed air whose temperature and humidityis adjusted to be constant. The regulator 42 adjusts the compressed airsupplied from the air source 40 to maintain it at a constant pressure.The compressed air maintained at a constant pressure by the regulator 42is supplied to the air supply channel 30 of the measuring table body 24via the A/E converter 44.

The compressed air supplied to the air supply channel 30 is injected anddischarged through the inner periphery of the work W held on themeasuring table 20. The A/E converter 44 converts the back pressure ofthe compressed air into an electrical signal using a built-in bellowsand differential transformer and outputs it to the controller 46. Then,the controller 46 calculates the inner diameter dimension of the work Waccording to the electrical signal. The calculated inner diameterdimension is displayed on a monitor 46A installed on the controller 46and is stored as data in a memory (not shown) installed in thecontroller 46.

The feeding unit 12 supplies the works W to be measured. It is equippedwith a feeding table 48 for housing a large number of works W to bemeasured. The feeding table 48 is provided, for example, with a platewhich has a large number of holes at certain intervals in the uppersurface. Each of the holes can contain a work W to be measured.

The recovery unit 14 recovers the works W which have been measured. Therecovery unit 14 comprises an OK item recovery table 50A for housing OKworks (works which meet a predetermined criterion) and an NG itemrecovery table 50B for housing NG works (works which do not meet thepredetermined criterion). The recovery tables 50A and 50B are providedwith a plate which has a large number of holes at certain intervals inthe upper surface as is the case with the feeding table 48. Each of theholes can contain a work W which has been measured.

The master storage unit 16 stores masters M used for zero calibrationand magnification calibration of the air micrometers 22. It comprises amaster storage table 52 for storing the masters M. The master storagetable 52 is provided, for example, with a plate which has a large numberof holes at certain intervals in the upper surface as is the case withthe feeding table 48. Each of the holes can contain one master.

The transport unit 18 transports the works W to be measured from thefeeding unit 12 to the measuring unit 10 and transports measured works Wfrom the measuring unit 10 to the recovery unit 14. It also transportsthe masters M from the master storage unit 16 to the measuring unit 10and transports calibrated masters M to the master storage unit 16. Thetransport unit 18 is equipped with a transfer robot 54. The transferrobot 54 comprises a vehicle 58 which travels along a guide rail 56installed on a ceiling frame (not shown), an extendable arm 60 mountedon the vehicle 58, and an openable/closable hand 62 attached to the tipof the arm 60. Each work W is transported, being gripped by the hand 62.

The control unit 70 controls individual units which compose the innerdiameter measuring device according to a preset motion program. It isequipped with a touch panel (not shown) as a means of entering variousinformation.

The inner diameter measuring device, configured as described above,operates as follows. For the purposes of explanation, it is assumed thatferrules manufactured to an outside diameter size of 2.5 mm and innerdiameter dimension of 0.125 mm have their inner diameter dimension dmeasured, accepted or rejected according to the results of measurements,and collected separately according to acceptance or rejection.Specifically, the works which satisfy a preset criterion are collectedas OK works on the OK item recovery table 50A while the works which donot satisfy the criterion are collected as NG works on the NG itemrecovery table 50B.

Before the works W are measured, the air micrometers 22 are calibrated,i.e., they undergo zero calibration and magnification calibration. Thecalibrations are performed when an execute calibration signal is inputin the control unit 70.

First, the control unit 70 takes the zero calibration master M out ofthe master storage unit 16 and transports it to the measuring unit 10 byoperating the transfer robot 54. The master M transported to themeasuring unit 10 is delivered and held to the measuring table 20.

To hold the master M, the master M is inserted in the work passage hole36 of the pressing ring 26, the grip of the transfer robot 54 isreleased, and then the pressing ring 26 is pressed toward the measuringtable body 24 by the pressing device (not shown). Consequently, theretaining ring 28 is squeezed by the pressing ring 26 and the master Mis held onto the measuring table 20 being gripped by the squeezedretaining ring 28.

When the master M has its tip inserted and held in the work receivinghole 34, a gap is formed between the master M and work receiving hole34, but it is sealed by the retaining ring 28 which is squeezed. Thus,all the air supplied to the air supply channel 30 is delivered to theinner periphery of the master M.

When the master M is held on the measuring table 20, the air source 40is operated and the compressed air whose pressure is adjusted to beconstant by the regulator 42 is supplied to the air supply channel 30 ofthe measuring table 20 via the A/E converter 44. The compressed airsupplied to the air supply channel 30 is discharged after passingthrough the inner periphery of the master M. The back pressure of thecompressed air is detected by the A/E converter 44 and output as anelectrical signal to the controller 46. The controller 46 stores theback pressure data of the zero calibration master M outputted as theelectrical signal in the built-in memory.

When the zero calibration master M has been measured, the air supply isstopped and the master M is unlocked. That is, the pressing ring 26 isfreed from being pressed by the pressing device and from being clampedby the retaining ring 28. The unlocked master M is removed from themeasuring table 20 and stored at its original location in the masterstorage unit 16 by the transfer robot 54.

Next, the transfer robot 54 takes the magnification calibration master Mout of the master storage unit 16 and transports it to the measuringunit 10. The master M transported to the measuring unit 10 is similarlydelivered and held to the measuring table 20. When the magnificationcalibration master M is held on the measuring table 20, the air source40 is operated again and compressed air is supplied to the air supplychannel 30 of the measuring table. The compressed air supplied to theair supply channel 30 is similarly discharged after passing through theinner periphery of the master M. The back pressure of the compressed airis detected by the A/E converter 44 and output as an electrical signalto the controller 46. The controller 46 stores the back pressure data ofthe magnification calibration master M outputted as the electricalsignal in the built-in memory.

When the magnification calibration master M has been measured, the airsupply is stopped and the master M is unlocked. The unlocked master M isremoved from the measuring table 20 and stored at its original locationin the master storage unit 16 by the transfer robot 54.

The controller 46 determines relationship (back pressure characteristic)between changes in inner diameter dimensions and changes in backpressures according to the acquired back pressure data of the zerocalibration master M and the magnification calibration master M as wellas on known inner diameter dimension data of the masters M. Also, itsets the measured value of the back pressure of the zero calibrationmaster M as a reference value for measurement.

Subsequently, the inner diameter dimensions d of works are measured bydetecting deviations in back pressure from the zero calibration masterM.

As described above, the zero calibration master M and magnificationcalibration master M have their inner diameter dimensions measuredaccurately in advance and the operator enters these values beforehand inthe controller 46 (via the touch panel (not shown) of the control unit70). The zero calibration master M and magnification calibration masterM have different inner diameter dimensions (minor norm and major norm).

This ends the calibrations of the air micrometer 22. Incidentally, theinner diameter measuring device according to this embodiment is equippedwith a plurality of the air micrometers 22, and all of them arecalibrated. When all the air micrometers 22 have been calibrated, theworks W are started to be measured.

First, the transfer robot 54 takes the work W to be measured out of thefeeding unit 12 and transports it to the measuring unit 10. The work Wtransported to the measuring unit 10 is delivered and held to themeasuring table 20.

To hold the work W, as is the case with the holding of the masters Mdescribed above, the work W is inserted in the work passage hole 36 ofthe pressing ring 26, and then the pressing ring 26 is pressed towardthe measuring table body 24 by the pressing device (not shown).Consequently, the retaining ring 28 is squeezed by the pressing ring 26and the work W is held on the measuring table 20, being gripped by thesqueezed retaining ring 28. At the same time, the gap between the work Wand work receiving hole 34 is sealed.

When the work W is held on the measuring table 20, the air source 40 isoperated, and compressed air whose pressure is adjusted to be constantby the regulator 42 is supplied to the air supply channel 30 of themeasuring table 20 via the A/E converter 44. The compressed air suppliedto the air supply channel 30 is discharged after passing through theinner periphery of the work W. The back pressure of the compressed airis detected by the A/E converter 44 and output as an electrical signalto the controller 46.

The controller 46 calculates the inner diameter dimension d of the workW according to the electrical signal from the A/E converter 44. That is,it calculates the inner diameter dimension d of the work W from thecalculated back pressure according to the back pressure characteristicdetermined in advance. The calculated inner diameter dimension d isdisplayed on the monitor 46A installed on the controller 46 and isstored as data in the memory (not shown) installed in the controller.

This ends the inner diameter dimension measurement of one work W. Whenthe measurement is finished, the operation of the air source 40 stopsand the measuring table 20 releases the work W. That is, the pressingring 26 is freed from being pressed by the pressing device (not shown)and from being clamped by the retaining ring 28 to unlock the work W.The unlocked work is removed from the measuring table 20 and transportedto the recovery unit 14 by the transfer robot 54.

Since the recovery unit 14 is equipped with the OK item recovery table50A for housing OK works and NG item recovery table 50B for housing NGworks, the recovered work W is stored in either the OK item recoverytable 50A or NG item recovery table 50B according to the results ofmeasurements. Specifically, the control unit 70 determines whether theinner diameter dimension d of the recovered work W satisfies the presetcriterion. If the work W satisfies the criterion, it is stored in the OKitem recovery table 50A, but if it does not satisfy the criterion, it isstored in the NG item recovery table 50B.

The above processes complete the measurement operation of one work. Assimilar operations are repeated, all the works W stored in the feedingtable 48 of the feeding unit 12 are measured. Since the inner diametermeasuring device according to this embodiment has a plurality of themeasuring tables 20, 20, . . . in the measuring unit 10, it proceedswith measurements while supplying works W one after another to thesemeasuring tables 20, 20, . . . In other words, works W are supplied oneafter another to the measuring tables 20, 20, . . . in such a way as tomake up for each work which finishes being measured. This makes itpossible to operate the transfer robot 54 efficiently, eliminatingwaiting time for measurements, and thus achieve efficient measurements.

In this way, the inner diameter measuring device according to thisembodiment supplies compressed air to the inner periphery of a work andmeasures the inner diameter dimension d of the work W according tochanges in the back pressure of the compressed air. This method canmeasure the inner diameter dimension of the work without rotating ormoving the work W, and thus can take measurements in a short time. Also,it can make device compact because it does not need a mechanism forrotating or moving the works.

Also, the this embodiment can effectively measure the inner diameterdimensions of even fine-diameter works such as ferrules because it doesnot insert a probe in the work unlike conventional methods which employscontact type displacement gauges. In this way, since the inner diametermeasuring device according to this embodiment takes non-contactmeasurements of inner diameter dimensions, it is especially useful inmeasuring the inner diameter dimensions of fine-diameter works.Especially, it is useful in measuring dimensions of fine cylindricalworks such as ferrules ranging from 0.05 mm to 1 mm in inner diameter.

Also, the inner diameter measuring device according to this embodimentis especially useful in measuring the inner diameter dimensions of longthin works such as ferrules, i.e., works W which have large axiallengths in relation to their outside diameter sizes. That is, as shownin FIG. 3, generally a ferrule has an internal chamfer C on an end, andwhen compressed air is supplied to the inner periphery of a chamferedwork W, the back pressure may not be measured correctly due to theinfluence of the chamfer C. However, when the axial length L is largeenough in relation to the outside diameter size D, even if there is aninternal chamfer C on an end, its effect can be eliminated and stablemeasurements can be ensured. Thus, preferably, the work W to be measuredsatisfies the relationship L/d>5, where d is the inner diameterdimension and L is the length.

Incidentally, although this embodiment recovers measured works in therecovery unit 14 by sorting them into OK works and NG works, it isalternatively possible to divide them more finely into ranks.

Also, although according to this embodiment, the measuring unit 10 isequipped with a plurality of the measuring tables 20, it isalternatively possible to provide only one measuring table 20. However,by installing a plurality of the measuring tables 20 as with thisembodiment, it is possible to measure a plurality of works Wefficiently.

Next, description will be given of a second embodiment of the method anddevice for measuring inner diameter dimension of works according to thepresent invention.

This embodiment concerns another calibration method for the airmicrometers 22 in the above described inner diameter measuring device.

As described above, since the method and device for measuring innerdiameter dimension of works according to the present invention takenon-contact measurements, it is useful in measuring the inner diameterdimensions of fine-diameter works.

However, as the diameter of the work W to be measured gets smaller, itbecomes more difficult to make masters.

Thus, in this embodiment, description will be given of a method forcalibrating the air micrometers 22 using masters which have someuncertainties.

First, a plurality of masters M which have some uncertainties areprepared. In this case, assuming that the works to be measured are 0.05mm to 1 mm in inner diameter, a plurality of masters M which haveuncertainties on the order of 0.5 μm are prepared.

The calibration involves measuring the back pressures of the pluralityof masters M which have the uncertainties and calculating an appropriateback pressure characteristic from measurement results using the leastsquares method.

In this way, by calculating an optimum value using a plurality ofmasters which have some uncertainties and a statistical technique suchas the least squares method, it is possible to take accuratemeasurements, reducing the effect of the uncertainties contained in themasters.

The method for measuring the optimum value is not limited to the leastsquares method. Various statistical techniques are available includingthose which involve taking an average of measured values.

These masters M are stored in the master storage table 52 of the masterstorage unit 16 and transported one by one to the measuring tables 20 bythe transfer robot 54.

Next, description will be given of a third embodiment of the method anddevice for measuring inner diameter dimension of works according to thepresent invention.

With the inner diameter measuring device of the above embodiments, themasters M stored in the master storage unit 16 are transported to themeasuring tables 20 by the transfer robot 54 to calibrate the airmicrometers 22. This embodiment provides a method for calibrating theair micrometers 22 without transporting the masters M. Incidentally,except for the calibration mechanism, the configuration of thisembodiment is the same as the inner diameter measuring device of theabove embodiments, and thus, only the calibration mechanism will bedescribed here.

FIG. 4 is a block diagram showing the calibration mechanism. As shown inthe drawing, a zero calibration master measuring table 80 andmagnification calibration master measuring table 82 are installed nearthe measuring table 20. The zero calibration master measuring table 80and magnification calibration master measuring table 82 have the sameconfiguration as the measuring table 20. Thus, each of them comprisesthe measuring table body 24, pressing ring 26, retaining ring 28, andpressing device (not shown), where the master is held by the retainingring 28 which is squeezed by the pressing ring 26.

The air supply channels 30, 30, and 30 of the measuring tables 20, 80,and 82 are connected with branch pipes 84A, 84B, and 84C, respectively.All the branch pipes 84A, 84B, and 84C are connected to a switching unit86. The switching unit 86 is supplied with compressed air from the airsource 40 via the regulator 42 and A/E converter 44 and supplies thecompressed air selectively to the branch pipe 84A, 84B, or 84C. In otherwords, the switching unit 86 selectively switches the destination of thecompressed air supplied from the air source 40. This switching isperformed according to a drive signal from the control unit 70.

The calibration mechanism, configured as described above, operates asfollows.

First, the transfer robot 54 takes the zero calibration master M out ofthe master storage unit 16 and transports it to the measuring unit 10.The zero calibration master M transported to the measuring unit 10 isdelivered and held to the zero calibration master measuring table 80.

Next, the transfer robot 54 takes the magnification calibration master Mout of the master storage unit 16 and transports it to the measuringunit 10. The magnification calibration master M transported to themeasuring unit 10 is delivered and held to the magnification calibrationmaster measuring table 82.

When the masters are held on the master measuring tables 80 and 82, theair source 40 is operated, and compressed air whose pressure is adjustedto be constant by the regulator 42 is supplied to the switching unit 86via the A/E converter 44.

Here, the switching unit 86 is connected to the zero calibration mastermeasuring table 80, and the compressed air is supplied to the zerocalibration master measuring table 80. The compressed air supplied tothe zero calibration master measuring table 80 is discharged afterpassing through the inner periphery of the zero calibration master M andthe back pressure of the compressed air is detected by the A/E converter44. The detected value of the back pressure is output as an electricalsignal to the controller 46. The controller 46 stores the back pressuredata of the zero calibration master M outputted as an electrical signalin the built-in memory.

When the zero calibration master M has been measured, the air supply isstopped. Then, the switching unit 86 switches the destination of thecompressed air from the zero calibration master measuring table 80 tothe magnification calibration master measuring table 82. In this state,the air source 40 is operated again, and compressed air whose pressureis adjusted to be constant by the regulator 42 is supplied to theswitching unit 86 via the A/E converter 44. Then, it is supplied to themagnification calibration master measuring table 82 via the switchingunit 86. The compressed air supplied to the magnification calibrationmaster measuring table 82 is discharged after passing through the innerperiphery of the magnification calibration master M and the backpressure of the compressed air is detected by the A/E converter 44. Thedetected value of the back pressure is output as an electrical signal tothe controller 46. The controller 46 stores the back pressure data ofthe magnification calibration master M outputted as an electrical signalin the built-in memory.

This ends the measurements of the zero calibration master M andmagnification calibration master M. The controller 46 determinesrelationship (back pressure characteristic) between changes in innerdiameter dimensions and changes in back pressures according to themeasured back pressures of the zero calibration master M andmagnification calibration master M as well as on known inner diameterdimension data of the masters M. Also, it sets the measured value of theback pressure of the zero calibration master M as a reference value formeasurement.

The above processes complete the calibrations of the air micrometers 22.Then, the switching unit 86 changes its connection from themagnification calibration master measuring table 82 to the measuringtable 20. Consequently, works W are measured one after another on themeasuring table 20.

In this way, the calibration mechanism according to this embodimentmakes it possible to calibrate the air micrometers 22 easily by simplyswitching the destination of compressed air. Calibrations need to beperformed periodically to maintain measurement accuracy, and thecalibration mechanism of this embodiment can perform calibration in ashort time because it does not need to change masters M. This makes itpossible to reduce the time spent on calibrations greatly and improveprocessing efficiency.

When the work W to be measured is changed, so are the zero calibrationmaster M and magnification calibration master M which are mounted on thezero calibration master measuring table 80 and magnification calibrationmaster measuring table 82, accordingly.

Next, description will be given of a fourth embodiment of the method anddevice for measuring inner diameter dimension of works according to thepresent invention.

The inner diameter measuring device according to this embodiment differsfrom the inner diameter measuring device of the first embodiment in thatit is further equipped with an air-leak checking mechanism. Otherwise,the configuration of this embodiment is the same as the inner diametermeasuring device of the first embodiment described above, and thus, onlythe air-leak checking mechanism will be described here.

FIG. 5 is a longitudinal section of the measuring table 20 equipped witha sealing device 90 for checking for air leaks. As shown in the drawing,the measuring table body 24 is flanked by a vertical column 92. On topof the column 92 is a motor 94, whose output shaft 94A is fitted with anarm 96. The arm 96 is mounted at right angles to the output shaft 94A.It oscillates between a sealing position (indicated by a solid line inFIG. 5) and waiting position (indicated by a two-dot chain line) whenthe motor 94 is operated. The tip of the arm 96 is fitted with a rubberpad 98 in disk shape, which is pressed against the top face of the workor master held on the measuring table 20, thereby sealing the upper endof the inner periphery of the work or master.

The work or master has its inner periphery sealed by the rubber pad 98when the arm 96 is located at the sealing position, and has it unsealedwhen the arm 96 is located at the waiting position.

The sealing device 90 configured as described above can be used to checkfor air leaks as follows.

The work W transported to the measuring unit 10 by the transfer robot 54is held on the measuring table 20.

As described above, the work W is held on the measuring table 20 withits tip inserted in the work receiving hole 34. The gap formed betweenthe work W and work receiving hole 34 is sealed by the retaining ring28.

Thus, if the work W is held securely, the air supplied from air supplychannel 30 will not leak. However, if the work W is not held properly,air may leak from between the work W and work receiving hole 34.

Therefore, when the work W is held to the measuring table 20, it ischecked for air leaks as follows to make sure that it is held securelyon the measuring table 20.

First, when the work W is held to the measuring table 20, the motor 94is operated and the arm 96 swings from the waiting position to thesealing position. Consequently, the pad 98 attached to the tip of thearm 96 comes into contact with the upper end face of the work W held onthe measuring table 20 to seal the upper end of the inner periphery ofthe work W. In this state, the air source 40 is operated and compressedair is supplied to the air supply channel 30 of the measuring table 20.The back pressure of the compressed air is detected by the A/E converter44 and output as an electrical signal to the controller 46. Thecontroller 46 checks for air leaks according to back pressure outputtedas the electrical signal. Specifically, since any air leak will show upas a change in the back pressure, changes in the back pressure ischecked for, thereby to check for air leaks from the measuring table 20which holds the work W.

When the checking is finished, air supply stops, the motor 94 isoperated again, and the arm 96 returns to the waiting position. If it isdetermined that there is no air leak, normal measurements are takensubsequently.

On the other hand, if it is determined that there are air leaks, thework W is held anew. Specifically, the transfer robot 54 picks up thework W and holds it again to the measuring table 20. Then, air leaks arechecked for, using the same procedures as above. If it is determinedagain that there are air leaks, the measurement is stopped, suspectingan equipment failure, and a warning is issued (e.g., the warning isdisplayed on the monitor 46A or a buzzer is sounded). Consequently, theoperator performs a maintenance operation and the like according to thewarning.

In this way, since the inner diameter measuring device according to thisembodiment is equipped with the air-leak checking mechanism, it caneliminate wrong measurements caused by air leaks and always obtainaccurate measurements.

Incidentally, an air-leak check is made each time a measurement istaken, including measurements of the masters M.

Also, although according to this embodiment, the sealing device 90 isattached to the measuring table 20, mechanisms for sealing the upper endof the inner periphery of the work or master are not limited to this.For example, such a mechanism may be installed on the transfer robot 54.

Besides, the air-leak checking mechanism according to this embodimentcan be applied to the inner diameter measuring device of the second andthird embodiments as well as to the inner diameter measuring device ofthe first embodiment.

Next, description will be given of a fifth embodiment of the method anddevice for measuring inner diameter dimension of works according to thepresent invention.

The inner diameter measuring device according to this embodiment differsfrom the inner diameter measuring device of the first embodiment in thatit is further equipped with a mechanism for inspecting the end faces ofworks for flaws. Otherwise, the configuration of this embodiment is thesame as the inner diameter measuring device of the first embodimentdescribed above, and thus, only the mechanism for end-face flawinspection will be described here.

FIG. 6 is a longitudinal section of the measuring table 20 equipped withan end-face flaw detector 100. The end-face flaw detector 100 uses a CCDcamera to pick up images of an end face of a work W held on themeasuring table 20, and inspects the end face of the work for flawsaccording to the resulting image data.

As shown in FIG. 6, a CCD camera 102 is installed above the measuringtable 20. It is equipped with an AF lens unit 104. The AF lens unit 104,driven by an AF lens drive device (not shown), is focused on the endface of the work W held on the measuring table 20. Then, images of theend face of the work W is magnified by the AF lens unit 104 and pickedup by a CCD contained in the CCD camera 102.

The image data of the end face of the work W shot by the CCD camera 102is output to an image processing unit 106, which then processes theimage data to inspect the end face of the work for flaws.

Incidentally, the CCD camera 102 is moved between a waiting position andmeasuring position by a robot (not shown). It is usually located at aretracted position (the waiting position) away from the measuring table20 and moves to above the measuring table 20 only for flaw inspection.

The inner diameter measuring device with the above configurationaccording to this embodiment operates as follows.

When the work W is transported to the measuring unit 10 by the transferrobot 54 and held on the measuring table 20, its inner diameterdimension is measured using the procedures of the above embodiments.When the inner diameter dimension of the work W has been measured, theCCD camera 102 is moved from the waiting position to the measuringposition by the robot (not shown).

When the CCD camera 102 moves to the measuring position, the AF lensunit 104 is driven and focused on the end face of the work W held on themeasuring table 20. Then, images of the end face of the work W ismagnified by the AF lens unit 104 and picked up by a CCD contained inthe CCD camera 102.

The image data of the end face of the work W shot by the CCD camera 102is output to an image processing unit 106, which then processes theimage data to inspect the end face of the work for flaws.

After the inspection, the robot (not shown) is operated again and theCCD camera 102 returns to the waiting position.

The above processes complete the inner diameter measurements of the workW including the end-face flaw inspection. Then, the work W is recoveredto the recovery unit 14, being sorted according to the results of theinner diameter measurements including the results of the end-face flawinspection. In other words, the work W is recovered, being classifiedinto either an OK work or NG work.

In this way, the inner diameter measuring device according to thisembodiment can inspect the end faces of works for flaws in addition tonormal measurements of inner diameter dimensions. This eliminates theneed to inspect the end faces for flaws separately, and thus improvesthe efficiency of work product inspections.

Incidentally, although this embodiment only inspects the end face of thework for flaws according to image data of the end face of the work Wshot by the CCD, it is also possible to determine the outside diametersize of the work W, inner diameter dimension at its end face,eccentricity between the outside diameter and inner diameter dimension,etc. through image processing according to the image data.

Also, the end-face flaw detector 100 according to this embodiment can beapplied to the inner diameter measuring device of the second to fourthembodiments as well as to the inner diameter measuring device of thefirst embodiment.

INDUSTRIAL APPLICABILITY

As described above, the present invention can measure the inner diameterdimension of works without rotating the works, and thus can takemeasurements in a short time. Also, it can make device compact becauseit does not need a mechanism for rotating the works. Furthermore, italways gives accurate and stable measurements over a long period of usebecause non-contact measurements do not cause wear.

1. An inner diameter measuring method for measuring an inner diameterdimension of a cylindrical work without inserting a probe into thecylindrical work, comprising the steps of: supplying compressed air toan inner periphery of a cylindrical master whose inner diameterdimension is known, detecting its back pressure, and thereby calculatinga back pressure characteristic which represents a relationship betweenthe inner diameter dimension and the back pressure; and supplyingcompressed air to an inner periphery of the work to be measured,detecting its back pressure, and thereby measuring the inner diameterdimension of the work according to the back pressure characteristic. 2.The inner diameter measuring method as defined in claim 1, wherein thework is 0.05 mm to 1 mm in inner diameter.
 3. The inner diametermeasuring method as defined in claim 1, wherein an optimum value of theback pressure characteristic is calculated by a statistical techniqueusing a plurality of masters which have some uncertainties.
 4. The innerdiameter measuring method as defined in claim 1, wherein the step ofsupplying compressed air to an inner periphery of the work to bemeasured is performed sealingly engaging an end face of the work to bemeasured against a source of said compressed air with the innerperiphery of the work in communication with an externally positionedoutlet of a compressed air supply passage.
 5. An inner diametermeasuring device which measures an inner diameter dimension of acylindrical work without inserting a probe into the cylindrical work,comprising: a work holding device which holds a work or a master whoseinner diameter dimension is known; an air supply device which suppliescompressed air to an inner periphery of the work or master held by thework holding device; a back pressure detecting device which detects backpressure of the compressed air supplied by the air supply device to theinner periphery of the work or master; a back pressure characteristiccalculating device which calculates a back pressure characteristic whichrepresents a relationship between the inner diameter dimension and backpressure according to a detected value of the back pressure of themaster detected by the back pressure detecting device; and an innerdiameter calculating device which calculates the inner diameterdimension of the work from the back pressure of the work detected by theback pressure detecting device, according to the back pressurecharacteristic.
 6. The inner diameter measuring device as defined inclaim 5, wherein the work is 0.05 mm to 1 mm in inner diameter.
 7. Theinner diameter measuring device as defined in claim 5, furthercomprising: a work feeding device which feeds a work to be measured tothe work holding device; a work recovering device which recovers thework from the work holding device after measurement; and a sortingdevice which sorts works recovered by the work recovering device intopredetermined ranks according to calculation results produced by theinner diameter calculating device.
 8. The inner diameter measuringdevice as defined in claim 5, comprising a plurality of the work holdingdevices and back pressure detecting devices.
 9. The inner diametermeasuring device as defined in claim 5, further comprising: an imagepickup device which picks up an image of an end face of the work held bythe work holding device; and a flaw inspecting device which inspects anend face of the work for flaws according to the image of the end face ofthe work projected on the image pickup device.
 10. The inner diametermeasuring device as defined in claim 5, wherein said work holding devicecomprises a holding mechanism which is adapted for sealingly engaging anend face of the work to be measured against a source of said compressedair with the inner periphery of the work in communication with anexternally positioned outlet of a compressed air supply passage.
 11. Theinner diameter measuring device as defined in claim 10, wherein saidholding mechanism comprises a seal and a pressing mechanism forcompressing said seal into engagement with the outer periphery of thework and around the outlet of the compressed air supply passage.
 12. Aninner diameter measuring device which measures an inner diameterdimension of a cylindrical work, comprising: a work holding device whichholds a work or a master whose inner diameter dimension is known; an airsupply device which supplies compressed air to an inner periphery of thework or master held by the work holding device; a back pressuredetecting device which detects back pressure of the compressed airsupplied by the air supply device to the inner periphery of the work ormaster; a back pressure characteristic calculating device whichcalculates a back pressure characteristic which represents arelationship between the inner diameter dimension and back pressureaccording to a detected value of the back pressure of the masterdetected by the back pressure detecting device; and an inner diametercalculating device which calculates the inner diameter dimension of thework from the back pressure of the work detected by the back pressuredetecting device, according to the back pressure characteristic, whereinthe work holding device and/or the master holding device comprises: aholding device body in which a work receiving hole is formed to insertthe work or master along an axis: an elastically deformable retainingring which is installed at an opening of the work receiving hole andthrough which the work or master is inserted in the work receiving hole;a pressing member which is capable of going in and out of the holdingdevice body through the retaining ring and which presses the retainingring against the holding device body and thereby causes the retainingring to deform elastically and contract its inner diameter; and an airsupply channel which is communicated with the work receiving hole andsupplies compressed air to the work receiving hole, wherein after thework or master is inserted in the work receiving hole through theretaining ring, the inner diameter measuring device clamps and fastensthe outer surface of the work or master in the work receiving hole withthe inner periphery of the retaining ring and seals the opening of thework receiving hole with the retaining ring by pressing the retainingring with the pressing device and causing the retaining ring to contractits inner diameter.
 13. The inner diameter measuring device as definedin claim 12, further comprising: a blocking device which blocks an openend of the work held by the work holding device and/or the master heldby the master holding device; and an air leak detecting device whichdetects leakage of air supplied to the work receiving hole of the workholding device according to the detected value of the back pressure ofthe work detected by the back pressure detecting device and/or detectingleakage of air supplied to the work receiving hole of the master holdingdevice according to the detected value of the back pressure of themaster detected by the back pressure detecting device.